Inner surface measuring apparatus

ABSTRACT

An inner surface measuring apparatus includes: a low coherent light source that outputs low coherent light; a low coherent light dividing section that divides one portion of the low coherent light; a light path length adjusting section that adjusts a light path length of one of the low coherent lights divided by the low coherent light dividing section; a straight rod shaped probe that irradiates the other of the low coherent lights divided from a front end section onto a measurement object; a low coherent light multiplexing section that multiplexes a low coherent light that returns having been reflected on the measurement object with the one low coherent light whose light path length has been adjusted by the light path length adjusting section; a light detector that detects the multiplexed low coherent light; and a rotation mechanism that relatively rotates the probe and the measurement object.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an inner surface measuring apparatus.

This application is based on Japanese Patent Application No.2005-218654, the content of which is incorporated herein by reference.

2. Description of Related Art

Conventionally, a surface state meter having a contacting probe is knownas an apparatus for measuring surface information of a measurementobject, such as surface roughness and contour shape, (for example,Mitutoyo Corporation, Product Information, Searched on 31 May 2005,Internet <URL:http://www.mitutoyo.co.jp/products/keijyou_hyomen/hyomen_(—)01.html>).

This surface state meter measures a contour shape and so forth of ameasurement object by making a contacting probe contact with the surfaceof the measurement object and relatively moving the contacting probe.Specifically, this surface state meter measures the contour shape and soforth of the measurement object by detecting an amount of movement ofthe contacting probe along the surface shape of the measurement object.

However, there are limits in measuring surface shape using thecontacting probe. For example, in the case of measuring the innersurface shape of a hole where a sectional area of the hole iscomparatively large and an inside diameter of the hole is unlikely tochange in the depth direction of the hole, it is possible to measure bymaking a small probe contact with the inner surface. However, in thecase where the sectional area of the hole is comparatively small and theinside diameter is small at the entry of the hole and becomes greaterfurther away from the entry in the depth direction, there is adisadvantage in that a small probe that can pass through the entrycannot make contact with the inner surface at the deeper end of thehole, making measuring difficult.

BRIEF SUMMARY OF THE INVENTION

In consideration of the heretofore known problems described above, anobject of the present invention is to provide an inner surface measuringapparatus that enables highly accurate measurement of an inner surfaceshape of a hole, in particular, an inner surface shape of a hole theentry of which is narrow and which becomes wider further in from theentry.

In order to achieve the above object, the present invention provides thefollowing means.

The present invention provides an inner surface measuring apparatuscomprising: a low coherent light source that outputs low coherent light;a low coherent light dividing section that divides one portion of thelow coherent light outputted from the low coherent light source in totwo; a light path length adjusting section that adjusts a light pathlength of one of the low coherent lights divided by the low coherentlight dividing section; a straight rod shaped probe that irradiates theother of the low coherent lights divided by the low coherent lightdividing section from a front end section onto a measurement objectarranged in a direction intersecting with the lengthwise direction ofthe probe; a low coherent light multiplexing section that multiplexes alow coherent light that returns having been reflected on the measurementobject with the one low coherent light whose light path length has beenadjusted by the light path length adjusting section; a light detectorthat detects the multiplexed low coherent light; and a rotationmechanism that relatively rotates the probe and the measurement objectabout an axis along the lengthwise direction of the probe.

According to the present invention, the front end of the probe isinserted into a hole that is the object of the measurement, the lowcoherent light source outputs low coherent light, and the outputted lowcoherent light is divided into two by the low coherent light dividingsection. The light path length of one of the divided low coherent lightsis adjusted by the light path length adjusting section. The other of thelow coherent lights enters into the probe, and is outputted from thefront end section of the rod shaped probe in a direction intersectingwith the lengthwise direction, and is irradiated on the measurementobject arranged in that direction. The other low coherent light isreflected on the measurement object and returns through the probe. Theother low coherent light, which has returned in this way, is multiplexedwith the one low coherent light, the light path length of which has beenadjusted, by the low coherent light multiplexing section. When the lightpath lengths of two of these coherent lights match with each other at ahigh level of accuracy, both of the low coherent lights interfere witheach other, resulting in a variation in a light amount of themultiplexed low coherent light that is detected by the light detector.Therefore, by monitoring a variation in the light amount detected by thelight detector while relatively rotating the probe and the measurementobject by the operation of the rotation mechanism, a distance from theprobe to the inner surface of the hole, which is the measurement object,can be measured at a high level of accuracy for the entire periphery.

The above invention may also comprise: an illumination light source thatoutputs illumination light; an illumination light multiplexing sectionthat is arranged between the probe and the multiplexing section and thatreceives the illumination light from the illumination light source alongan optical axis of the low coherent light; a light dividing section thatdivides the illumination light reflected on the measurement object fromthe low coherent light; an image pickup device that picks up the dividedreflected light; and a display device that displays an image obtained bythe image pickup device.

Thus, upon the operation of the illumination light multiplexing section,the illumination light emitted from the illumination light source isoutputted on the optical axis of the low coherent light and isirradiated together with the low coherent light on the measurementobject. The illumination light reflected on the measurement objectreturns into the probe together with the low coherent light. Thisreturned reflected light is divided from the low coherent light in thelight dividing section, and is picked up by the image pickup device andthe obtained image is displayed by the display device.

Thus, it becomes possible to carry out measurement of the surface shapewhile monitoring the surface status of the measurement object with theimage. Therefore, in the case where a rapid change or the like occurs inthe measurement values when measuring the surface shape, the surfacestatus can be confirmed with the image.

Furthermore, in the above invention, the illumination light source mayoutput an excitation light outside the sensibility of the image pickupdevice, and on the front end of the probe there may be provided afluorescent substance that generates visible light when excited by theexcitation light, and a reflection light multiplexing section thatmerges the visible light reflected by the measurement object with thelight path of the excitation light.

Thus, the excitation light, which has been emitted from the illuminationlight source and is outside the sensibility of the image pickup device,excites the fluorescent substance on the front end of the probe andgenerates the visible light, and the generated visible light illuminatesthe measurement object. The reflected light of the visible lightreflected on the measurement object is merged into the light path of theexcitation light by the reflection light multiplexing section andreturns, and it is divided by the light dividing section and picked upby the image pickup device, and the obtained image is displayed by thedisplay device.

In this case, since the excitation light is irradiated from theillumination light source, and the visible light is generated at thefront end of the probe, flare that occurs when the visible light travelsthrough each optical system can be suppressed compared to the case ofirradiating the visible light from the illumination light source. As aresult, a clear image having less flare can be displayed by the displaydevice.

Furthermore, in the above invention, on the illumination light sourceside of the fluorescent substance there may be arranged a visible lightreflection film that allows the excitation light to pass through whilereflecting the visible light.

Thus, the visible light generated by the fluorescent substance isreflected by the visible light reflection film and it is therebyprevented from returning to the illumination light source side and flareoccurrence can be suppressed, while an amount of the illumination lightto be irradiated on the measurement object can be increased and a brightand clear image can be obtained.

According to the present invention, an effect can be achieved such thatthe inner surface shape of a hole, in particular, the inner surfaceshape of a hole the entry of which is narrow and which becomes widerfurther in from the entry, can be measured at a high level of accuracy.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is an overall configuration diagram that schematically shows aninner surface measuring apparatus according to a first embodiment of thepresent invention.

FIG. 2 is a partially enlarged view showing a relationship between aprobe and workpiece of the inner surface measuring apparatus shown inFIG. 1.

FIG. 3 is a diagram that schematically shows the close proximity of theprobe of the inner surface measuring apparatus according to a secondembodiment of the present invention.

FIG. 4 is an overall configuration diagram showing a variant example ofthe inner surface measuring apparatus shown in FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

Hereunder is a description of an inner surface measuring apparatus 1according to a first embodiment of the present invention, with referenceto FIG. 1 and FIG. 2.

As shown in FIG. 1, the inner surface measuring apparatus 1 according tothe present embodiment is provided with: a rotation mechanism 4 thatholds a workpiece 3 having a hole 2 and rotates the workpiece 3substantially around a central axis of the hole 2; a probe 5 that isinserted into the hole 2 along the central axis of the hole 2; ameasuring apparatus main body 6 that measures an inner surface shape ofthe hole 2 by irradiating light via the probe 5 and detecting reflectedlight from the inner surface of the hole 2 of the workpiece 3; and anoptical fiber 7 that connects the probe 5 and the measuring apparatusmain body 6.

The rotation mechanism 4 is provided with a motor 9 fixed on a base 8,and a chuck 10 provided on a rotational shaft of the motor 9. Byoperating the motor 9 while the workpiece 3 is being held by the chuck10, the workpiece 3 can be rotated substantially around the central axisof the hole 2, and can be stopped at a predetermined angle position.

As shown in FIG. 2, the probe 5 is formed in a rod shape of a diameterthat allows the probe 5 to be inserted into the hole 2 of the workpiece3, and internally has a heterogeneous medium lens 11 that relays lowcoherent light L₀ (described later) entering from a rear end side of theprobe 5 along a lengthwise direction to a front end side, and a prism 12that deflects the low coherent light L₀ relayed to the front end through90 degrees and outputs it in a radial direction. The probe 5 is disposedin a position on the central axis of the workpiece 3 fixed on therotation mechanism 4, and is made so that its front end position can beshifted along the central axis by a rectilinear movement mechanism 13.

The measuring apparatus main body 6 comprises: a coherent light source14 that outputs the low coherent light L₀; a collimator lens 15 thatmakes the low coherent light L₀ outputted from the coherent light source14 into substantially parallel light; a half mirror 16 that divides thelow coherent light L₀, which has been made into parallel light, into areference light L₁ and a measuring light L₂ and that multiplexes thereturned measuring light L₂ and reference light L₁; coupling lenses 18and 19 that collect the reference light L₁ and the measuring light L₂and input them into one end of optical fibers 7 and 17; a mirror 20disposed on the other end side of the optical fiber 17, that reflectsthe reference light L₁ that has been propagated through the inside ofthe optical fiber 17; a mirror moving mechanism 21 that moves the mirror20 in a light-axis direction; a light detector 22 that detects amultiplexed low coherent light L₃; and a shape extraction section 23that extracts the inner surface shape of the hole 2 of the workpiece 3based on a light amount of the low coherent light L₃ detected by thelight detector 22 and on information of a rotational angle position ofthe workpiece 3 from the rotation mechanism 4, and based on informationof an axial direction position from the rectilinear movement mechanism13. In the diagram, reference symbol 24 denotes a collimator lens,reference symbol 25 denotes a condensing lens, and reference symbol 26denotes a monitor.

In the present embodiment, lengths of the optical fibers 7 and 17 areset to substantially equalize light path lengths of the measuring lightL₂ and reference light L₁, which have been divided by the half mirror16.

Hereunder is a description of the operation of the inner surfacemeasuring apparatus 1 according to the present embodiment which isconfigured as described above.

In order to measure an inner surface shape of the hole 2 of theworkpiece 3 using the inner surface measuring apparatus 1 according tothe present embodiment, first, the workpiece 3 is held by the chuck 10of the rotation mechanism 4 so that it can be rotated substantiallyaround the central axis of the hole 2 by operation of the motor 9.Subsequently, the probe 5 is inserted into the hole 2 of the workpiece 3by operation of the rectilinear movement mechanism 13, and the axialdirection position of the front end of the probe 5 is adjusted.

In this state, the low coherent light source 14 outputs the low coherentlight L₀. Having been made into substantially parallel light by thecollimator lens 15, the low coherent light L₀ is partially transmittedthrough, and partially reflected by, the half mirror 16. The portion ofthe low coherent light that has been transmitted is used as themeasuring light L₂. The portion of the low coherent light that has beenreflected is used as the reference light L₁.

The measuring light L₂ is input into one end of the optical fiber 7 bythe coupling lens 18, and having been propagated inside the opticalfiber 7, is input into the rear end of the probe 5. In the probe 5, themeasuring light L₂ is relayed to the front end by the heterogeneousmedium lens 11 and then deflected through 90 degrees by the prism 12arranged on the front end, and output in the outward radial direction.

The inner surface of the hole 2 of the workpiece 3 is disposed in theoutward radial direction of the probe 5. Consequently, the measuringlight L₂ reflected by the inner surface of the hole 2 returns into theprobe 5, and returns into the measuring apparatus main body 6 via theprism 12, the heterogeneous medium lens 11, and the optical fiber 7.

The measuring light L₂ that is returned into the measuring apparatusmain body 6 is made into substantially parallel light by the couplinglens 18, and then reflected by the half mirror 16 and collected by thecondensing lens 25 and detected by the light detector 22.

Meanwhile, the reference light L₁ reflected by the half mirror 16 isinput into one end of the optical fiber 17 by the coupling lens 19, andis propagated through the optical fiber 17. Subsequently, the referencelight L₁ is output from the other end of the optical fiber 17, and ismade into substantially parallel light by the collimator lens 24, thenreflected by the mirror 20. By being reflected by the mirror 20, thereference light L₁ returns via the collimator lens 24, the optical fiber17, and the coupling lens 19, and is transmitted through the half mirror16 and collected by the condensing lens 25, and detected by the lightdetector 22.

The light path length of the measuring light L₂ and the light pathlength of the reference light L₁ are set to be substantially equal. Inthe case where the light path lengths of the measuring light L₂ and thereference light L₁ differ from each other, interference between thereference light L₁ and the measuring light L₂ does not occur, and atotal light amount is detected by the light detector 22. On the otherhand, by moving the mirror 20 by operation of the mirror movingmechanism 21, the reference light L₁ and the measuring light L₂interfere with each other in a position where the light path length ofthe measuring light L₂ matches the light path length of the referencelight L₁ at high level of accuracy.

When the reference light L₁ and the measuring light L₂ interfere witheach other, an interference fringe occurs and the light amount detectedby the light detector 22 rapidly increases or decreases as a result.Therefore, with the rotation mechanism 4 and the rectilinear movementmechanism 13 stopped in predetermined positions so that the relativepositions of the workpiece 3 and probe 5 are fixed, by finding aposition where the light amount detected by the light detector 22rapidly increases or decreases by moving the mirror 20 by operation ofthe mirror moving mechanism 21 to change the light path length of thereference light L₁, the position where the light path lengths of thereference light L₁ and the measuring light L₂ match each other can belocated.

A geometrical light path length of the measuring light L₂ from the lowcoherent light source 14 to the front end of the probe 5 is fixed.Therefore, in the shape extraction section 23, a distance from the frontend of the probe 5 to the inner surface of the hole 2 is accuratelycalculated by subtracting the light path length of the measuring lightL₂ to the front end of the probe 5 from the light path length of thereference light L₁ in the position where the light path lengths of thereference light L₁ and the measuring light L₂ match each other.Moreover, in the shape extraction section 23, the calculated distancefrom the front end of the probe 5 to the inner surface is associatedwith angle position information of the rotation mechanism 4 and axialdirection position information of the rectilinear movement mechanism 13and stored.

Then, in this state, the rotation mechanism 4 is operated, and it isstopped when the workpiece 3 has rotated only by a very small angle withrespect to the probe 5. By repeatedly carrying out the above measuringoperation, a distance from the front end of the probe 5 in apredetermined axial direction position to the inner surface of the hole2 is obtained for the entire periphery.

Next, the rectilinear movement mechanism 13 is operated, and it isstopped when the probe 5 has moved with respect to the workpiece 3 inthe axial direction only a very small distance. By repeatedly carryingout the above measuring operation for the entire periphery, the innersurface shape of the hole 2 can be measured within a predeterminedrange.

According to the present embodiment, the inner surface shape is measuredusing interference of low coherent lights L₁ and L₂ without a contactingprobe. Accordingly, the probe 5 is constructed in a thin shape to enablemeasurement of the inner surface shape of a hole 2 of a small diameterat a high level of accuracy. Moreover, there is the further advantagethat an inner surface shape of a hole 2, the small diameter of whichbecomes greater the further in from the entry, can also be measured at ahigh level of accuracy.

Furthermore, in the inner surface measuring apparatus 1 according to thepresent embodiment, with the probe 5 fixed with respect to the workpiece3, the mirror 20 is moved to measure the distance between the probe 5and the inner surface of the hole 2, and this measurement is repeated.Instead of this, the measurement may be carried out by maintaining therotation of the workpiece 3 with respect to the probe 5 by the operationof the rotation mechanism 4 and by slightly moving the mirror 20 by theoperation of the mirror moving mechanism 21. This way has the advantagethat a plurality of circumferential positions at which the distancebetween the probe 5 and the inner surface of the hole 2 are equal can bedetected in a short period of time, and a length of time required formeasuring can be reduced.

Moreover, in the present embodiment, the workpiece 3 is rotated whilethe probe 5 is fixed. Alternatively, the probe 5 may be rotated whilethe workpiece 3 is fixed. Furthermore, in the present embodiment, theprobe 5 is moved in the axial direction with respect to the workpiece 3.Alternatively, the workpiece 3 may be moved in the axial direction whilethe probe 5 is fixed.

Furthermore, in the present embodiment, the low coherent light L₀ isdivided into the reference light L₁ and the measuring light L₂, and asingle half mirror is employed as a member for multiplexing thereference light L₁ and the measuring light L₂. Alternatively, a lowcoherent light dividing section and a low coherent light multiplexingsection may be separately provided.

Next, an inner surface measuring apparatus 30 according to a secondembodiment of the present invention is described, with reference to FIG.3.

In the description of the present embodiment, similar reference symbolsare given to the parts that are common to the configuration of the innersurface measuring apparatus 1 according to the first embodiment, andtheir descriptions are omitted.

As shown in FIG. 3, an inner surface measuring apparatus 30 according tothe present embodiment comprises: an illumination light source 31 thatoutputs visible light L₄ for illumination to the rear end of a probe 5;a multiplexing prism (illumination light multiplexing section) 32 thatinputs the visible light L₄ from the illumination light source 31 intothe light path of a measuring light L₂; a dividing prism (light dividingsection) 33 that separates from the light path of the measuring lightL₂, the visible light that has been reflected on the inner surface ofthe hole 2 of the workpiece 3 and returned; and an image pickup device34 that picks up the divided visible light L₄. Reference symbols 35 and36 denote condensing lenses in the diagram.

In the inner surface measuring apparatus 30 according to the presentembodiment having such a configuration, the visible light L₄ emittedfrom the illumination light source 31 is input by the multiplexing prism32 into the probe 5, and emitted from the front end of the probe 5together with the measuring light L₂. The emitted visible light L₄illuminates the inner surface of the hole 2 and the reflected light L₄thereof returns into the probe 5. The reflected light L₄ that returnsinto the probe 5, travels backward through the probe 5, and is separatedfrom the light path of the measuring light L₂ by the dividing prism 33and is picked up by the image pickup device 34. As a result, an image ofthe inner surface of the hole 2 within the area in close proximity tothe position on which the measuring light L₂ is irradiated, can beobtained.

Therefore, in the inner surface measuring apparatus 30 according to thepresent embodiment, when measuring the inner surface shape of the hole 2of the workpiece 3, it becomes possible to obtain an image of the statusof the inner surface of the hole 2 being measured, and the status of theinner surface can be observed while carrying out inner surfacemeasuring. Therefore, for example in the case where a peculiar innersurface shape is determined while measuring, the status of this locationcan be further observed.

Moreover, in the case where the measuring light L₂ to be used formeasuring is visible light, the spot light of the measuring light L₂ canbe visually checked in the image. Therefore the measuring position andthe inner surface shape therein can be associated and confirmed withinthe image. On the other hand, in the case where the measuring light L₂to be used for measuring is invisible light, the spot light thereofcannot be visually checked. In this case, for example, if a sight isdisplayed in the center of the image by pre-adjusting the measuringlight L₂ so as to be irradiated on the central position of the displayedimage, the position on which the measuring light L₂ is irradiated can beconfirmed in the image.

Moreover, in the present embodiment, an illumination light source 31that outputs visible light L₄ for illuminating the inner surface of thehole 2 is employed. Instead of this, as shown in FIG. 4, theillumination light source 31 may output invisible (wavelength bandwidthoutside of the sensibility of the image pickup device 34) excitationlight L₅, and a fluorescent substance 37 that emits fluorescent light L₆when excited by the excitation light L₅ may be arranged on the front endof the probe 5. In FIG. 4, reference symbol 39 denotes a fluorescencemultiplexing prism that merges the returned fluorescent light L₆, whichhas been reflected in the hole 2, with the light path of the measuringlight L₂ of the probe 5.

As the excitation light L₅ emitted from the illumination light source 31travels through the heterogeneous medium lens 11 inside the probe 5 andis irradiated from a prism 12 on the front end of the probe 5 towardsthe inner surface of the hole 2, it is incident on the fluorescentsubstance 37 to generate a fluorescent light L₆. The generatedfluorescent light L₆ illuminates the inner surface of the hole 2 and thereflected light L₆ that has been reflected and returned returns into theprobe 5, and is then separated from the light path of the measuringlight L₂ by the dividing prism 33, and is picked up by the image pickupdevice 34.

In this way, compared to the case where visible light L₄ from theillumination light source 31 travels through the probe 5 and is emittedfrom the front end of the probe 5 and is reflected on the inner surfaceof the hole 2 and travels backward inside the probe 5, since thefluorescent light L₆, which is visible light, only needs to travel inthe probe 5 in one returning direction, the occurrence of flare in theoptical system inside the probe 5 can be prevented. As a result, thereis an advantage of obtaining a clear image, while preventing theoccurrence of flare on the obtained image.

In this case, it is preferable to arrange a fluorescent reflection film38 that allows the excitation light L₅ to pass through while reflectingthe fluorescent light L₆, on the light source side of the fluorescentsubstance 37. Since the fluorescent light L₆ generated in thefluorescent substance 37 is reflected by the fluorescent reflection film38, the generated fluorescent light L₆ can be prevented from directlyreturning into the probe 5, while increasing the light amount of thefluorescent light L₆ that illuminates the inner surface of the hole 2.Accordingly, there is an advantage of obtaining a bright image.

1. An inner surface measuring apparatus comprising: a low coherent lightsource that outputs low coherent light; a low coherent light dividingsection that divides one portion of the low coherent light outputtedfrom the low coherent light source in to two; a light path lengthadjusting section that adjusts a light path length of one of the lowcoherent lights divided by the low coherent light dividing section; astraight rod shaped probe that irradiates the other of the low coherentlights divided by the low coherent light dividing section from a frontend section onto a measurement object arranged in a directionintersecting with the lengthwise direction of the probe; a low coherentlight multiplexing section that multiplexes a low coherent light thatreturns having been reflected on the measurement object with the one lowcoherent light whose light path length has been adjusted by the lightpath length adjusting section; a light detector that detects themultiplexed low coherent light; a rotation mechanism that relativelyrotates the probe and the measurement object about an axis along thelengthwise direction of the probe; an illumination light source thatoutputs illumination light; an illumination light multiplexing sectionthat is arranged between the probe and the low coherent lightmultiplexing section and that receives the illumination light from theillumination light source along an optical axis of the low coherentlight; a light dividing section that divides the illumination lightreflected on the measurement object from the low coherent light; animage pickup device that picks up the divided reflected light which isseparated from the low coherent light by the light dividing section; anda display device that displays an image obtained by the image pickupdevice.
 2. An inner surface measuring apparatus according to claim 1,wherein the illumination light source outputs an excitation light whichhas a wavelength bandwidth that cannot be sensed by the image pickupdevice, and on the front end of the probe there is provided afluorescent substance that generates visible light when excited by theexcitation light, and a reflection light multiplexing section thatmerges the visible light reflected by the measurement object with thelight path of the excitation light.
 3. An inner surface measuringapparatus according to claim 2, wherein on the illumination light sourceside of the fluorescent substance there is arranged a visible lightreflection film that allows the excitation light to pass through whilereflecting the visible light.